There are two IP modes supported in a cdma2000® wireless IP network. These are the so-called simple IP (SIP) and mobile IP (MIP). Details of CDMA wireless IP are provided in TIA IS-835. The standard is known in Third Generation Partnership Project 2 (3GPP2) as X.S0011. The mobile IP section of the IS-835 standard refers in turn to the Internet Engineering Task Force (IETF) standard named RFC2002. Some cdma2000-based wireless IP networks support both MIP and SIP. Others support only SIP or only MIP. Regardless of the operation mode, the network and the mobile device establish and configure the point-to-point protocol (PPP) as described in RFC1661 to establish a packet data session. An “always-on” mobile device always maintains PPP connectivity even when it does not have radio link layer connectivity to the network. When the device or network does not have any data to send, the packet data service on the mobile device enters a “dormant” state. The PPP connectivity between the network and the device is maintained, but the physical radio connection is torn down in such a state. Note that cdma2000® is a registered trademark of the Telecommunications Industry Association (TIA-USA).
In a SIP-based wireless IP network, mobile devices are assigned geographically dependent IP addresses dynamically by the visited Packet Data Serving Nodes (PDSN). As the mobile device moves it will be assigned a new geographically dependent IP address. If the mobile device supports any “push” applications such as Push e-mail, then it is the responsibility of the mobile device to notify the associated push servers whenever its IP address as assigned by the wireless network changes. In a SIP-based network, mobile devices may not know how long the IP address is assigned for. The PDSN may tear down the PPP session and reassign the IP address to another mobile device if it has not heard from the mobile device upon the expiration of an assigned IP address duration. A PDSN may unilaterally tear down the PPP session if the mobile fails to respond to page messages while out of coverage even if the PPP session time has not expired. This will break push services as the mobile device is no longer associated with the IP address that the push servers are aware of. As a result, “Always-on” mobile devices in a SIP session need to send periodic “keep alive” packets to maintain PPP connectivity.
In a mobile IP network, each mobile device is typically assigned a static IP address by its home agent (HA) which is then maintained by the mobile terminal regardless of its geographical point of attachment. As the mobile moves, it registers with a foreign agent (FA) which provides a care-of-address (COA). The home agent is informed of the mobile device's COA through the registration procedure. The foreign agent maintains a binding of Home IP address to care-of-address. The home agent receives packets for the terminal and forwards these to the foreign agent according to the care-of-address such that the mobile device remains reachable via its geographically-independent IP address. Because of this, a MIP terminal will always be reachable. The network notifies the mobile of the duration of the address and as such the mobile terminal will know the expiry time of assigned address. As long as the mobile device re-registers before this timer expires, the PPP connectivity is maintained.
Mobile IP provides a number of other advantages over simple IP such as multiple user profiles with different user ID/password etc. This allows a single mobile device to have multiple user accounts. The IS-835 standard only states that if a wireless terminal fails to establish a mobile IP session, it should fall back to SIP mode to establish a SIP data session. The standard does not state any mechanism how a “dormant” mobile device in a SIP session can establish a MIP session when it visits a network that supports MIP.
For the purpose of illustration, shown in FIG. 1 is an example of a cdma2000 wireless IP network as described in IS-835. There is a wireless simple IP network 10 and a wireless mobile IP network 12.